Many rubber articles are reinforced with textiles that are made of filamentous materials. Textile reinforced rubber articles have improved strength and durability as compared to rubber articles without any reinforcement. This reinforcement allows rubbers to be used in more demanding applications, such as ones where the rubber article is subjected to considerable movement, high friction, and temperature extremes. Reinforced rubbers are commonly found in vehicle and airplane tires, conveyor and engine belts, and hoses.
Formaldehyde resin/latex-based adhesives are frequently used for adhering a reinforcing textile to rubber. The adhesive materials are able to establish strong adherence between the textile and rubber materials through a combination of physical and chemical interactions. For example, the latex adhesive layer forms encapsulating structures and holds the fibers of the reinforcing material and rubber particles together. The strong adherence between the materials facilitated by the adhesive provides a layered composite that is tough and durable, and prevents mechanical failure of the rubber article.
Adhesives providing good bonding properties have been prepared from vinyl-pyridine rubber latex reacted with resorcinol formaldehyde to form a condensate. The vinyl pyridine content in a latex polymer can provide chemical characteristics that promote excellent adhesive properties in rubber reinforcing applications.
One disadvantage, however, is that vinyl pyridine (VP) is an expensive starting material. Use of a VP-based adhesives significantly increases the price of a reinforced rubber article versus one that does not use a VP-based adhesive. On the other hand, reducing the amount of VP in the latex can reduce the adhesive properties of the latex, and lead to mechanical failure of the reinforced article.
One alternative approach to improve adhesion between the textile reinforcing portion and the rubber portion uses pre-coated fiber materials, such as polyester fibers coated with an epoxy compound. However, the additional materials and process steps involved can also increase product cost.
Another problem in the production of textile reinforced rubber articles is that encapsulation characteristics of a latex adhesive can limit the type of textiles used to produce well-reinforced rubber articles. For example, is difficult to adhere polyester to rubber with a resorcinol-formaldehyde resin latex adhesive. Nylon, on the other hand, is typically used as the reinforcing fabric because it permits strong adhesion between the resin of the latex adhesive composition through encapsulation. However, nylon may not be a desired reinforcing material for certain applications. For example, as compared with polyester, nylon is much more expensive as a reinforcing material. Also, some polyaramid textiles, such as Kevlar™ (like polyester), are difficult to adhere to rubber with a resorcinol-formaldehyde resin latex adhesive. Although many of these polyaramid textiles could potentially provide very strong reinforcements and would desirable for forming reinforced rubber articles, there use is limited by the latex adhesive systems of the prior art.